Metallic materials are known which comprise, imbedded in a matrix, aligned monocrystalline metallic monocarbide fibers of the formula MC, M being the metal and C the chemical symbol of carbon, formed by unidirectional solidification and the mechanical properties of which at high temperatures are well beyond those of standard super-alloys. Such composite materials have been the object of U.S. Pat. No. 3,871,835.
Such materials offer a very profitable route for technical applications at high temperatures.
In the aeronautic field for instance, where the desired increase for the performance of the gas turbines requires increasingly higher gas temperatures and rotation speeds, these materials offer decisive advantages for the manufacturing of the blades.
In this general program, complex composite materials with a very high strength have been developed, based on Ni, Fe and Co, the reinforcement being obtained by monocrystalline fibers in a monocarbide of a transition metal, such as TaC, NbC or TiC.
Materials particularly adapted for aeronautic use are Ni-based and their reinforcement is obtained with NbC fibers. They are practically insensitive to thermal cycling, viz. to repeated temperature variations in the operating conditions of aircraft.
As disclosed in U.S. Pat. No. 4,043,841 the compositions of said materials are within the following limits:
______________________________________ Cr 6 to 15% W 7 to 10% Al 3 to 6% Nb 4 to 6% C 0.4 to 0.65% Ni + Co balance to 100. ______________________________________
In said materials, the matrix, which is Ni- and Co-based, is hardened by the presence of tungsten in solid solution.
The matrix is also hardened by precipitation in its solid solution, or .gamma. phase, of an ordered .gamma.' phase of the Ni.sub.3 Al type.
It had been established that the resistance to the thermal cycling of such materials increases in proportion to the hardening of the matrix, viz. with increasing Al and W contents.
It has now been established that the precipitation in the solid solution of the ordered .gamma.' phase calls upon not only the Ni, but also upon one or several of the other elements present in the solid solution, whereby atoms of said elements can be substituted for the Ni atoms and the Al atoms in the lattice formed by the .gamma.', Ni.sub.3 Al phase. The phase obtained is in fact a phase of the .gamma.', (Ni,Xi).sub.3 (Al,Yi) type, Xi representing the various elements which have been substituted for Ni atoms in the lattice and Yi those which have been substituted for the Al atoms.
Thus, these materials comprise three phases, viz. a solid solution which is Ni- and Co-based, a .gamma.'(Ni,Xi).sub.3 (Al,Yi) precipitate--these two phases forming the matrix as such--and a third phase formed by the reinforcement fibers.